Laser Footprint Size and Pointing Precision Analysis for Lidar Systems

Laser footprint size and beam divergence angle tuning was found to affect LiDAR data accuracy and measurement precision because of beam axis shifting. The laser beam divergence angle is generally tunable in modern LiDAR systems in order to adapt to different application scenarios. Beam divergence angle can either be switched from one position to the other (i.e. 0.3mRad / 0.8 mRad), or be tuned continuously (i.e. 0.3 to 0.8 mRad). In either case, mechanical moving parts have to be introduced into the optical systems. As a result, the movements of mechanical parts make the optical axis shift and the laser pointing direction shift as well. In other words, switching laser beam divergence angle makes the laser pointing accuracy degrade. A mathematic model was developed to improve the LiDAR data accuracy when the laser beam divergence angle was changed in surveying practice. Experiments were designed and carried on to verify the calibration model. A calibration method and procedure was introduced to handle these issues.